The project is directed towards an increase in our understanding of biological membrane structure and function in three studies. Using model systems ranging from single walled bilayer vesicles of known dimensions to right side out and inside out vesicles prepared from human red cell membranes. I. Fluorescent probe studies of solute binding to lipid membranes. We have developed a method for measuring probe fluorescence in lipid bilayers at concentrations as low as one probe molecule per vesicle. We will first characterize the vesicle-probe interaction, including its temperature dependence, and will then determine the thermodynamic parameters for the interaction of vesicles with small nonelectrolytes and with proteins. II. Fluorescent probe studies on the mechanisms involved in the maintenance of human red cell membrane structure and shape. We have used our subnanosecond fluorimeter (SLM Instruments) to measure the overall fluidity of spectrin removal from the inside of the red cell membrane and will now study the deformability of spectrin itself. We will also continue our studies on the effect of Ca on membrane fluidity. III. Studies on calcium transport across inside out vesicles. We have shown that inside out red cell vesicles are relatively well sealed to alkali cations, and have developed a method to measure the cation flux. Permeation is affected by the addition of calcium to the outside surface of these vesicles; we plan to characterize the binding sites involved and the mechanism by which calcium controls permeation. BIBLIOGRAPHIC REFERENCES: Solomon, A.K. Thermodynamic aspect of nonelectrolyte permeation of lipid bilayers. Pontificiae Academiae Scientiarum Scripta Varia 40:(10) IV:1, 1976. Cohen, C.M. and Solomon, A.K. Ca binding to the human red cell membrane: characterization of membrane preparation and binding sites. J. Membr. Biol. 29: 345-372, 1977.